1. Field of the Invention
The present invention relates generally to the controlled heating of exposed heat-processable photosensitive media or material, such as so-called dry process or dry silver photosensitive or photographic material, for the purpose of heat processing the material. Such heat processing is done to develop the images which have been recorded on the material during its exposure. More specifically, the invention relates to that form of such heat processing wherein the material includes an electrically conductive backing, and wherein the heating of that material, which will be referred to hereinafter simply as material, is effected by passing an electric current through said backing.
2. Description Of The Prior Art
In carrying out the heat processing of material, as defined above, the heating current is passed through the backing of the material in such a manner that the material is heated to a so-called processing temperature for a certain period of time. That temperature and time are ones which have been found to give the desired degree of image development for the particular situation, and are usually based on time-temperature data furnished by the manufacturer of the material.
In one form of the known arrangements which provide such heat processing, the above-noted heating of the material to the desired temperature is achieved by applying the heating current to the material at a preselected value for a preselected period of time. This "programmed" method of heat processing has the disadvantage of requiring continuous adjustment to compensate for changes in certain factors. Those factors are the ones which determine how much heat must be generated in the material in a given situation in order that the correct processing temperature will be reached and maintained for the required time. A typical example of apparatus which effects the heat processing of moving material by this programmed method is the apparatus which is shown in the upper portion of FIG. 1 of the Gregg U.S. Pat. No. 3,887,787. A typical example of apparatus which effects the heat processing of individual pieces of material by a programmed method is the apparatus which is shown in the copending U.S. patent application of Dean M. Peterson, Ser. No. 891,077.
In another form of the known arrangements which provide heat processing, the heating current is passed through the backing of the material under the control of means which sense the degree of development of a test image which has been recorded on the material. An example of apparatus which operates in this manner is that which is shown in the lower portion of FIG. 1 of the above-noted Gregg patent. Such apparatus has the disadvantage of being relatively complex, due to the need for the means which produce and sense the test image. Such apparatus has the further disadvantage of producing improperly developed primary images until changes in the heating procedure are made by the apparatus following the detection of an imperfectly developed test image.
The foregoing description makes it clear that there has been a need for an improved heat processing method, and for improved apparatus which utilizes said method, which do not possess the above-noted shortcomings of the known heat processing methods and apparatus.